1. Field
Example embodiments relate to a driver, and for example, to a driver configured to reduce a driving signal distortion, and a semiconductor memory device having the driver.
2. Description of Related Art
A capacity of a memory device including a semiconductor memory device is ever-increasing. For example, a number of memory cells in a unit area of the semiconductor memory device are increasing. Generally, the semiconductor memory device includes a driver for driving the memory cells. For example, a dynamic random access memory (DRAM) device and a static random access memory (SRAM) device have a word-line driver for driving word-lines.
A driver may provide a driving signal (e.g. word-line selection signal) to drive the memory cells. The driving signal is distorted as the driving signal is transferred along the word-line from the driver because the number of the memory cells is relatively large. In other words, a transition time of the driving signal (e.g. a time for the driving signal to transit from logic “low” to logic “high”) is increased as the driving signal is applied farther away from the driver.
FIGS. 1 and 2 are block diagrams illustrating drivers using conventional methods of reducing a driving signal distortion.
The method of FIG. 1 reduces the driving signal distortion by increasing the size of the driver 110. For example, a larger driver 110 is connected to the loads 150. The method of FIG. 2 reduces the driving signal distortion by disposing buffers 220 between loads 250 (e.g. capacitors of a memory device). For example, buffers 220a and 220b are connected between the loads 250 connected to a driver 210.
FIG. 3 is an example graph diagram illustrating an example simulation result of drivers using the conventional method of FIG. 1 and the conventional method of FIG. 2. The horizontal axis denotes an elapsed time and the vertical axis denotes a voltage level.
A first curve 310 indicates the simulation result at a load LOAD_n 150 connected to the driver 110 using the method of reducing a driving signal distortion by increasing a size of the driver 110. A second curve 320 indicates the simulation result at a load LOAD_n 250 connected to the driver 210 using the method of reducing a driving signal distortion by disposing the buffer 220 between the loads.
In case of the driver 110 using the method of reducing the driving signal distortion by increasing the size of the driver 110, a square wave pulse is improperly formed because a driving signal more gradually transits from logic “low” to logic “high”, and more rapidly transits from logic “high” to logic “low”. However, a time distortion of the driving signal occurs less noticeably if the driving signal transits from logic “low” to logic “high”.
In case of the driver 210 using the method of reducing the driving signal distortion by disposing the buffer 220 between the loads, a time distortion (i.e. a delay time) occurs because of the buffer 220. However, the driving signal is similar to the square wave pulse.